Polymers and copolymers of the nu-pyridyl imide of maleic and citraconic acids



Patented Aug. 17, 1954 POLYMERS AND COPOLYMERS OF THE N-PYRIDYL IMIDE OF MALEIC AND CITRACONIC ACIDS Gaetano F. DAlelio, Pittsburgh, Pa., assignor to Koppers Company, Inc., a corporation of Delaware N Drawing. Application August 31, 1951, Serial No. 244,694

21 Claims.

This invention relates to new monomers and to new polymeric materials derived therefrom and is particularly directed to the polymerization products obtained by polymerizing a mass comprising an N-pyridyl imide maleic or citraconic acid and a copolymerizable compound especially acrylonitrile. The invention also relates to compositions of these polymerization products adapted to the formation of shaped articles, in many cases to molecularly oriented shaped articles, particularly to fibers, threads, bristles, mono-filaments, etc., hereinafter referred to as fibers, and other shaped articles such as films and the like, which articles show improved dyeing properties.

It has been known for sometime that certain copolymers of acrylonitrile may beadapted to the preparation of shaped articles, such as films, fibers, foils, tubes, etc. Some of these copolymers have been regarded as capable of being cold-drawn to produce structures molecularly oriented along the fiber axis. Cold-drawing may be defined as the stretching of a polymeric material at a temperature below the melting point of the material to give a molecularly oriented structure.

The resistance of acrylonitrile polymers to dyes of all types has presented serious dyeing problems, especially in the development of synthetic fibers from these polymers. In fact, in order to dye polyacrylonitrile one commercial process resorts to the use of high pressures with water solutions or organic dispersions of dyes. It has been proposed that improvement in dye susceptibility can be obtained by the use of itaconic acid in small amounts as acopolymerizing monomer in the preparation of acrylonitrile polymers. However, the polymer products obtained thereby have a tendency to .crosslink upon standing at temperatures of at least about 70-80 C. or upon spinning from hot solutions. causes spoliation ofmaterial by gelatin during storage, embrittlement of fibers, fouling of spinning jets, and other production difficulties.

In accordance with the present invention it has now been found that improvements in dyeing Such crosslinking properties of acrylonitrile polymers are obtained by the polymerization of monomeric masses comprising acrylonitrile and an N-pyridyl imide of maleic or citraconic acid (i. e., the imide formed from an amino pyridine and maleic or citraconic acid or anyhdride) with or without other copolymerizable ethylenic compounds. It has been found further that in addition to the fact that the N-pyridyl imides of maleic and citraconic acids yield particularly valuable copolymers with acrylonitrile, they may also be used effectively to form copolymers with other types of copolymerizable ethylenic compounds having a CH2=C group. Thus it has been found that valuable polymerization products may be prepared in accordance with the invention by polymerizing a monomeric mass comprising N-pyridyl imide of maleic or citraconic acid and a polymerizable compound such as acrylonitrile and the other polymerizable ethylenic compounds listed. hereinafter.

The N-pyridyl imides of maleic and citraconic acids of this invention may be represented by the formula oH-oo in which R is hydrogen or the methyl group and P is a pyridine nucleus. The pyridine nucleus may be substituted or unsubstituted. If substimore than a total of 5 carbon atoms as in the case of the monoethyl pyridines, the dimethyl pyridines, the diethyl pyridines, the methyl ethyl pyridines, isoquinoline, quinoline, and the alkylated quinolines such as quinaldine.

The N-pyridyl imides of maleic and citraconic acids themselves are readily prepared by reacting the amino pyridines with maleic or citraconic anhydride and thereafter effecting ring closure by heating alone or in the presence of acetic anhydride. For example, 2 pyridyl N maleic imide can be prepared by heating Z-amino pyridine with maleic anhydride in the presence of ether and evaporating the ether to form the intermediate acid amide whose structure is and then distilling the intermediate acid amide to eifect ring closure.

The proportions of the imide in the polymerization products of the invention may vary over a wide range, ranging from equimolar proportions of imide downto very small amounts of imide such as maybe employed in acrylonitrile polymers to impart dye susceptibility thereto. Although even smaller amounts are somewhat effective, the improvement in susceptibility of acrylonitrile copolymers to dyes becomes particularly noticeable when the imide content of the copolymer is about 0.1 per cent and the susceptibility increases as the amount of imide is increased. Ordinarily sufficient improvement in dye susceptibility is obtained with amounts of imide ranging up to about or per cent but it may be advantageous for reasons such as in the preparation of ion-exchange polymers or as additives to improve dyeing properties to have a larger proportion of imide in the acrylonitrile copolymer. In such cases the concentration of imide may range up to or approaching 50 mole per cent. Within these proportions acrylonitrile copolymers of the invention show great afilm'ty toward many dyes especially acidic and vat dyes.

In addition to the improvements effected in the resulting copolymers, the use of N-pyridyl imides of maleic and citraconic acids has certain other advantages over the use of the corresponding acids. For example, the imides are more soluble in acrylonitrile than the acids and therefore it is easier to get complete copolymerization of the imide with acrylonitrile in solution, emulsion and suspension polymerizations.

The acrylonitrile copolymers discussed herein are soluble in N,N-dimethyl acetamide (DMA), N,N-dimethyl formamide (DMF), butyrolactone,

ethylene carbonate, N,Ndimethyl methyl urethane of the formula (CH3)2NCOOCH3, ethylene carbamate, N-methyl-2-pyrrolidone, and a number of similar solvents, used alone or in conjunction with N,N-dimethyl cyanamide, N,N-dimethyl cyano-acetamide, N,N-dimethyl methoxy-acetamide, methylene dinitrile, methylene di-thiocyanate, formyl caprolactam, formyl morpholine, tetramethylene sulfone, etc. Nitroalkanes, such as nitromethane, may be used as solvents for such copolymers having no more than about 85 per cent acrylonitrile, providing the comonomers used in preparing such copolymers do not have substituent groups of equal or greater secondary bonding force than the cyano groups in acrylonitrile. copolymers of the present invention which have high proportions of monomers of relatively low secondary-valence bonding strength, such as vinyl chloride, may often be dissolved in acetone or mixtures of acetone and solvents of the above types.

This invention will be more fully described by the following examples which illustrate methods of practicing the invention. In these examples and throughout the specification, parts and percentages are intended to mean parts by weight and percentages by Weight.

Example I y onitrile idy1) Polym Maleic Imide parts of water (20:1 bath-fiber ratio).

4 to 50 C. for 24 hours. Steam is then introduced into the reactor to remove unpolymerized monomer or monomers from the mixture. A small amount of aluminum sulfate is added to the mixture and the polymer is isolated by filtration.

The polymer is then washed with water and with methyl alcohol. A portion of the polymer is dissolved in demethyl formamide or butyrolactone and a film cast from the solution. The film is washed entirely free of solvent and stretched at a ratio of about 8:1 in a glycerine bath at to C. The film is then washed in water and dyed in a bath containing for each part of film 0.05 part of 1,5-diamino-4,8-dihydroxyanthraquinone-B-sulfonic acid, 0.03 part sulfuric acid and 50 parts Water (50:1 bath-film ratio) at boiling temperature for one hour. The film is then removed and washed with water and secured for 15 minutes in a 0.4 per cent soap solution at 85 C. Whereas the unmodified polyacrylonitrile when treated in this manner has little or no color, all of the copolymers are dyed to a deep blue shade. :Fibers are spun from the same solutions either by dry spinning, or by wet spinning. The fibers are substantially freed from solvent and dried. After the dried fibers have been cold-drawn 600- 900 per cent at 120-145 C. and subsequently heat-treated at C. for one hour, the fibers are given the same dyeing and washing treatment described above with the same results as for the films, a light tint being acquired by the unmodified polyacrylonitrile fibers and a deep and dense color being given to the copolymer fibers. The polymers of this example are also soluble in dimethyl formamide, dimethyl acetamide, tetramethyl urea, butyrolactone, ethylene carbonate, formyl morpholine, etc.

Example II Five parts of the copolymer fiber C of Example I is dyed to a deep green shade using the vat color, dimethoxy-dibenzanthrone, at 70 C. in a bath containing 0.5 part of dye, 0.2 part sodium hydroxide, 0.5 part sodium hydrosulfite and 100 After the first 15 minutes of heating, 0.25 part of Glaubers salt was added. The sample is then oxidized in a 0.5 per cent sodium dichromate-1.0 per cent acetic acid aqueous solution at 70 C. for 30 minutes in a 20:1 bath-fiber ratio. The dyed fiber is then scoured in a boiling 0.5 per cent soap solution. A sample of yarn prepared from the unmodified acrylonitrile polymers and dyed under the same conditions acquires only a light shade of color.

If 1,5-di-p-anisoy1amino-4,8-dihydroxyanthraquinone is used as the vat dye, th copolymer fiber is dyed a strong violet color.

Example III The procedure of Example I is repeated for the polymerization of the following monomer compositions:

Parts To 900 parts of water, adjusted to a pH of about three, in a suitable reactor, is added 1.0 part of ammonium persulfate, 0.5 part of sodium bisulfite, and. 100 parts of monomer or monomer mixture. The reactor is then flushed with deoxygenated nitrogen and heated with agitation N(2- Acrylo- Vinyl pyrid 1) O0 01 er Solub P1Ymer nitrile Chloride Maiei c p E Imide' Parts Parts Parts 92 5 3 DMF, DMA, etc. 87 10 3 DMF, DMA, etc. 82 15 3 DMF, DMA, etc. 77 20 3 NOzMe. 57 40 3 NOzMe. 37 60 3 Acetone.

Sometimes copolymers D and E, when dissolved in nitromethane may have gelled, partially dissolved particles known as fisheyes. In such cases, the solubility maybe improved by the addition of small amounts of materialswhich are good.

Example IV The procedure of Example I is repeated forthe polymerization of the following monomer compositions: l

Po y nmne gimme Maleic Imide PL Pg Pt.

Dyeing tests of these copolymers show improvements in dye susceptibility similar to'Example I. In place. of styrene, various styrene derivatives may be used, such as alpha-methyl-styrene;

nuclear-substituted chloro-styrenesi. e., ortho-, meta-, and pararchloro-styrenes, dichlo'ro-styrenes, for example, the 2,3-, 2.4-, 2,5-, 2,6-, 3.4-, and 3,5-dichloro-styrenes, trichloro-styrenes;

cyano-styrenes, such as ortho-, meta-, and para- Example V The procedure of Example I is repeated for the polymerization of the following monomer compositions:

N-Quin- Vmyli- Acryloolyl Copolymer Soluble Polymer dene mtnle Maleic In- Chloride Imide Pt. Pt. Pt. i

85 5 l0 DMF, DMA, etc. 65 25 l DMF, DMA,etc. 45 45 10 DMF, DMA, etc. 25 65 10 DMF, DMA, etc. 5 85 DMF, DMA, etc.

With the above vinylidene chloride copolymers and similar copolymers having a total of acrylonitrile and vinylidene chloride of at least 85 per cent in the polymer molecules, only the more active solvents, su-chyas ;butyrolactone, ethylene 6 carbonate, N,N-dimethyl acetamide, N,N-dimethyl formamide, N,N,N',N-tetramethyl urea, etc., can be used as solvents. The above copolymers dye more readily and thoroughly than similar copolymers containing no maleic imide of an amino pyridine.

Example VI The procedure of Example I is repeated for the polymerization of the following monomer compositions Vinyli- (N -Pyridyl) Acrylo- Vinyl Polymer dene Oitracomc nitrile Chloride Chloride Imide Pt. Pt. Pt. Pt.

The dyeing tests of the copolymer products show dye susceptibility similar to the copolymers of Example I.

Instead of copolymerizing the N-pyriolyl imides of maleic or citraconic acids directly with the acrylonitrile, the imides may first be copolymerized with part of the acrylonitrile or with another monomer and this independently prepared copolymer used to modify polyacrylonitrile or acrylonitrile copolymers. These modifying copolymers may be prepared substantially in accordance with the procedure of Example I and thereafter placed in solution and added to a solution of polyacrylonitrile, so that a composition consisting of sufficient polymeric N pyridyl imide resultsand satisfactory dyeing is obtained. As examples, polymers D and E of Example I may be used as modifiers for the unmodified homopolymers and copolymers of acrylonitrile. For example, polymer E of Example I, which consists of 80 parts of acrylonitrile and 20 parts of N (2- pyridyl) maleic imide has excellent compatibility with homcpolymers of acrylonitrile. In many cases, it is desirable to use the copolymers of the N-pyridyl imide, which have even a higher ratio of the imide, for example, as high as equal molar parts of the imide may be copolymerized with acrylonitrile or methacrylonitrile. Suitably from 10 to 15 to about 70 per cent of imide may be used. The overall amounts of imide required to improve the dyeability generally corresponds to the amounts indicated above for copolymers in Which the main body of the acrylonitrile polymers contain the imide copolymerized directly therein, that is, from at least about 0.1 per cent to advantageously 5 per cent or even up to 15 per cent imide in the ultimate polymer mixture. The copolymers of these imides with other monomers are also satisfactory such as, for example, copolymers of styrene, alpha-methyl-styrene, methyl acrylate, ethyl methacrylate, etc.

When it is desired to modify an acrylonitrile copolymer such as the copolymer of acrylonitrile and styrene or the copolymers of acrylonitrile and other copolymerizable ethylenic compounds, it is usually desirable to use as modifiers copolymers containing at least one structural unit present in the acrylonitrile copolymer. Thus asjthere are present in the acrylonitrile copolymer, structural units derived from the acrylonitrile and styrene, it is desirable to have present in the modifying copolymer structural units derived from styrene and/or acrylonitrile, advantageously both, in addition to those derived from the imide. BY time including in the modifying copolymers structural units of the same type as the structural units of the copolymer to be modified, greater compatibility between the acrylonitrile copolymer to be modilied and the modifying copolymer is obtained and the two are more readily soluble in the mutual solvent and will more readily mix into homogeneous polymer mixtures.

The polymerization products of the present invention have in the polymer molecule a plurality of repeating units of the formula in which R and P are as indicated above, and these products will contain additional repeating units of the formula when the imide is copolymerized with acrylonitrile.

In addition, the polymerization products of this invention may contain any number of repeating units of the type obtained by the copolymerization of an N-pyridyl imide of maleic or citraconic acid, or a mixture containing acrylonitrile and such an imide, with one or more copolymerizable ethylenic compounds, such as, for example, vinylidene chloride, vinyl chloride, styrene, alpha-methyl-styrene and methacrylonitrile. When the polymerization mass contains in addition to the imide, a polymerizable monomer having a CH2:C group in an amount such that the latter monomer is present to an extent of at least 50 mole per cent of the overall monomer content, then monomers such as fumaronitrile, beta cyano acrylamide and methyl beta-cyano-acrylate may also be present in the polymerization mixture.

As previously indicated, the solvent resistance of such copolymers as contain one or more monomer units in addition to those formed by the acrylonitrile and the N-pyridyl maleic or citraconic imide is affected by the type and proportion of copolymerizing monomer or monomers used to replace part of the acrylonitrile. For example, copolymers containing small amounts of N -pyridy1 maleic or citraconic imide units may contain various proportions of such monomer units as obtained from vinylidene chloride, methacrylonitrile, fumaronitrile, and beta-oyano-acrylamide without considerable reduction in solvent resistance. Replacement of acrylonitrile units in the copolymers by vinyl chloride, styrene and alpha-methyl-styrene units results in copolymers of lowered solvent resistance, the amount of such lowering in resistance in each case depending on the amount substituted. In addition to the solvent resistance, certain other physical properties of the copolymers are affected by the presence of these additional units in th copolymers. The amount and character of the changes in physical properties of these copolymers depend again on the type and proportion of copolymerizing monomer or monomers used. For example, the tensile strength of an acrylonitrile N-pyridyl maleic or citraconic imide type copolymer will decrease much more when a monomer having relatively weak secondary bonding forces, such as styrene or ethylene is used to replace part of the acrylonitrile than when one or more monomers having relatively 8.. strong bonding forces, such as methacrylonitrile, fumaronitrile, beta-cyano-acrylamide, methyl beta-cyano-acrylate and vinylidene chloride is used to replace part of the acrylonitrile. Moreover, the ability of these copolymers to form molecularly oriented shaped articles depends on the type and amount of the copolymerizing monomer or monomers used to replace acrylonitrile.

Other copolymerizable ethylenic compounds, which may also be present in the polymerizable masses for copolymerization with the pyridyl maleic imides of this invention include one or more of the following: acrylates, e. g. methyl acrylate; methacrylates, e. g. methyl methacrylate; acrylamides, methacrylamides; vinyl esters, such as vinyl acetate; itaconic diesters, such as dimethyl and diethyl itaconates; itaconamide; vinyl halides, such as 'vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, trifluorochloroethylene; vinyl aryls, such as vinyl naphthalenes and the nuclear-substituted styrenes listed in Example IV, etc.

The polymerization products of this invention may be prepared by various polymerization systems, such as emulsion, suspension, mass and solution polymerizations. In addition to the monomer, the polymerizable mass may also contain other materials such as catalysts, e. g. peroxides, such as benzoyl peroxide, naphthyl peroxides, phthalyl peroxide, .tertiary-butyl-hydroperoxide, hydrogen peroxide, cyclohexyl hydroperoxide, tertiary-butyl perbenzoate, etc., azo catalysts, persulfates, such as ammonium persulfate, etc., solvents, suspension or emulsion media, emulsifying agents, suspension agents, plasticizers, lubricants, etc.

Foruse in the preparation of shaped articles, the polymerization products of this invention have molecular weights preferably of at least about 10,000. However, polymerization products of molecular weights less than 10,090 may be used for other purposes, such as impregnants, solvent resistant coatings, etc. The molecular weight of the polymerization products is dependent on the concentrations of the monomers, theamount and type of catalyst, the temperature of reaction etc.

As is quite generally known in the field of high polymers, molecular orientation is usually indicated and identified by birefringence of polarized light, as under Nicol prisms, by increased density as compared to the density of the same polymer unoriented, and by characteristic X-ray diffraction patterns. When a material is crystalline or oriented, its X-ray diagram shows bright areas or spots for points of crystallization and dark areas for the non-crystalline regions. The intensity or number of these bright spots increases with the degree of orientation or crystallization. Amorphous or non-crystalline materials give X- ray diagrams having very few high lights or bright spots whereas crystalline or oriented materials give definite X-ray diffraction patterns. In these patterns there are definite relationships of the bright spots with regard to position and spacing which are generally characteristic of the composition of the material being X-rayed. In fibers or films the orientation usually follows the direction of drawing or stretching sothat the orientation is parallel to the fiber axis or a major surface.

Useful fibers may be made from the solutions of the copolymers of this invention by dry spinning, as in the preparation of cellulose acetate fibers, or by wet spinning, as in the preparation of viscoserayon. In wet spinning, the solution n w i i.

of copolymer may bespun into a substance which is a non-solvent for the copolymer, but which is advantageously compatible wi'th the solvent in which the copolymer is dissolved. For example, water, acetone, methyl alcohol, carbon disulfide, glycerine, chloroform, carbon tetrachloride, benzene, etc., may be used as a precipitating bath for N,Nclimethyl acetamide, N,N,N',N'-tetramethyl urea, butyrolactone, ethylene carbonate, and other solvent compositions of these copolymers. The extruded fibers, from which substane tially all of thesolvent has been removed in. the spinning step, about 1-10 per cent remaining in the shaped article, may then be colddrawn about 100-900 per cent, preferably about 300-600 per cent; and the drawn fiber heattreated, usually at substantially constant length, at about LOO-160 C. to effect further erystallizationand removal of the remaining solvent. The term heat-treated, as used herein, refers to the ap" plication of heat toan object, usually at a controlled temperature and usually by means of the medium surrounding the object.

Many of the acrylonitrile copolymers of this invention may be molecularly oriented, especially if there is no more than 15 per cent N-pyridyl imide in the polymer molecule. This is true when the major portion of the copolymer is acrylonitrile, for example, 85 per cent or more acrylonitrile, or when the other copolymerizing monomers used in making such copolyniers have substituent groups having secondary valence bonding forces equal to or greater than exhibited by theficyano group in acrylonitrile. For example, if such monomers as methacrylonitrile, fumaronitrile, vinylidene chloride, beta-cyano-acrylamide and methyl beta-cyano-acrylate are used with acrylonitrile and the pyridyl imide, the proportion of acrylonitrile in the copolymers may be much less than 85 per cent without destroying the capacity for molecular orientation. Molecularly oriented, cold-drawn, shaped articles of particular usefulness are prepared from copolymer compositions containing in the polymer molecules 6099.9 per cent acrylonitrile, 01-15 per cent, advantageously 0.1 per cent, N pyridyl imide, with or without one or more monomers Ofthe class consisting of vinylidene chlo ride, vinyl chloride, styrene, alpha-methyl-styrene, methacrylonitrile, fumaronitrile, betacyano-acrylamide and methyl beta-cyanoacrylate, the eifects of the presence'of the monomers of this class being noticeable when the monomer is present in the polymer molecule in amounts of 1 per cent or more.

The polymerization products of, this. invention show great affinity for the acetate, acidic and vat dyes. The cellulose acetate dyes which are particularly products are mainly aminoeanthrauuinone derivatives. A number of other acidic dyes that can be used are anthranilio acid* 1-(4'-sulfophenyl) 3 methyl 5 pyrazolone; 1,5 ellamino 4%,8 dihydroxyanthraquinone 3 sulionic acid; 1 aminonaphthalene 4 n sulfonic acid-aalpha-naphtholl sulfonic acid; the sodium salt of sulfanilic acid aniline- 2-benzoylamino-5-naphthol'7-sulfonic acid; the sodium salt of 4,4 diaminostilbene 2,2 di sulfonic aCid:(phe!101)2 ethylated; 1,5-diamino-4,8,-dihydroxyanthraquinone-3-sulfonic acid; dye prepared by diazotizing l.-aminonaphthalene-4-sulfonic acid and coupled with alpha-naphtholisulfonic acid; the sodium salt of (maminobenzoic acidoanisidine) phosgenated; the soeiiective with these. polymerisation dium salt. of (2 naphthol' 6,8 disulfcnic acid ebenzidine-aphenol) ethylated; dimethoxydibenzanthrone; and 1,c-di-p-anisdylamino-4,8- dihydroxyanthraquinone.

From the molecularly orientable copolymers of this invention fibers may be prepared having improved dyeingproperties, low shrinkage in boiling Water, sometimes as low as 3 to 5 per centor less of the cold-drawn or stretched article, good heat resistance, and tensile strength in the order of a to 6 grams per denier; Moreover, these properites make the fibers desirable in the manufacture of hosiery and for such all-purpose fabrics. used for blouses, shirts, suits, etc.

What is claimedis:

1. The polymerization product obtained by" polymerizing a mass comprising an N-pyridyl imide of an acid selected from the class consisting of maleic and citraconic acids and a polymerizable monomer having a CH2=C group.

2. The composition of claim 1 in which the mass contains a polymerizable ethylenic compound selected from the class consisting of acrylonitrile, vinyl: chloride, vinylidene chloride, styrene, alpha -methyl-styrene, methacrylonitrile, fumaronitrile, beta cyano acrylamide, and methyl beta-cyano-acrylate.

3. The polymerization product obtained by polymerizing a mass comprising acrylonitrile and an N-pyridyl imide of an acid selected from the class consisting of maleic andcitraconic acids.

4. The copolymer of claim 2 in which. the imide is present in at least about 0.1 per cent of the polymerizable mass.

5. A polymeric composition having in the polymer molecule a plurality of repeating units having the formula of hydrogen and the methyl radical, and P is a pyridine nucleus inwhich the pyridine nucleus is unsubstituted except for hydrocarbon substituents containing a total of not more than .5 carbon atoms.

6. The polymeric composition of claim 5 which contains in the polymer molecule a plurality of repeating units of the formula 7. A polymerization product obtained by polymerizing a mass comprising an N-pyridyl imide of maleic acid, and a polymerizable monomer having aCHz=C group.

8., A polymeric composition having in the polymer molecule a plurality of repeating units having the formula 4311-011- 6 co o 9. The polymericcomposition of claim 8 which also contains in the polymer molecule a plurality of repeating units of the formula CHzCH- 10. A shaped article comprising a copolymer of acrylonitrile and an N-pyridyl imide of an acid selected from the class consisting of maleic and citraconic acids, said copolymer having a molecular weight of at least 10,000.

11. A cold-drawn shaped article having molecular orientation, said article comprising a copolymer of acrylonitrile and an imide having the following formula CH-CO in which R is selected from the class consisting of hydrogen and the methyl radical, and P is a pyridine nucleus in which the pyridine nucleus is unsubstituted except for hydrocarbon substituents containing a total of not more than carbon atoms, said copolymer having a molecular weight.

of at least about 10,000 and containing in the polymer molecule no more than about 15 per cent by weight of said imide.

12. A cold-drawn fiber having molecular orientation, said fiber comprising a copolymer of acrylonitrile and an N-pyridyl imide of maleic acid, said copolymer having a molecular weight of at least about 10,000 and containing in the polymer molecule no more than about 15 per cent by weight of said imide.

13. A cold-drawn fiber having molecular orientation, said fiber comprising a copolymer of about 68-989 per cent by weight acrylonitrile, about 0.1 to 5 per cent by weight an N-pyridyl imide of maleic acid, and about 1 to 39.9 per cent by weight of a compound selected from the class consisting of vinyl chloride, vinylidene chloride, styrene, alpha-methyl-styrene, methacrylonitrile, fumaronitrile, beta cyano acrylamide, and methyl beta-cyano-acrylate.

14. A cold-drawn fiber having molecular orientation, said fiber comprising a copolymer of about 60-989 per cent by weight acrylonitrile, about 0.1 to 5 per cent by weight an N-pyridyl imide of maleic acid, and about 1 to 39.9 per cent by weight vinylidene chloride.

15. A cold-drawn fiber having molecular orientation, said fiber comprising a copolymer of about 60-989 per cent by Weight acrylonitrile, about 0.1 to 5 per cent by weight an N-pyridyl imide of maleic acid, and about 1 to 39.9 per cent by Weight vinyl chloride.

16. A cold-drawn fiber having molecular orientation, said fiber comprising a copolymer of about 60-989 per cent by weight acrylonitrile, about 0.1 to 5 per cent by weight an N-pyridyl imide of maleic acid, and about 1 to 39.9 per cent by weight styrene.

17. A cold-drawn fiber having molecular orientation, said fiber comprising a copolymer of about 60-989 per cent by weight acrylonitrile,

beta-cyano-acrylate.

18. A cold-drawn fiber having molecular orientation, said fiber comprising a copolymer of about 60-989 per cent by weight acrylonitrile, about 0.1 to 5 per cent by weight of an imide having the following formula oH-oo 011-06 and about 1 to 39.9 per cent by weight of a compound selected from the class consisting of vinyl chloride, vinylidene chloride, styrene, alphamethyl-styrene, methacrylonitrile, fumaronitrile, beta-cyano-acrylamide, and methyl beta-cyanoacrylate.

19. A cold-drawn fiber having molecular orientation, said fiber comprising a copolymer of about 60-989 per cent by weight acrylonitrile, about 0.1 to 5 per cent by weight of an imide having the following formula and about 1 to 39.9 per cent by weight of a compound selected from the class consisting of vinyl chloride, vinylidene chloride, styrene, alphamethyl-styrene, methacrylonitrile, fumaronitrile, beta-cyano-acrylamide, and methyl beta-cyanoacrylate.

20. A polymerization product of 995-50 parts acrylonitrile and 0.1-50 parts N- (2 -p-yridy1) maleic imide.

21. The polymerization product of 92-37 parts acrylonitrile, 5-60 parts vinyl chloride and 3 parts N-(2-pyridyl) maleic imide.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,313,565 McDowell et al. Mar. 9, 1943 2,508,860 Grimmel May 23, 1950 

1. THE POLYMERIZATION PRODUCT OBTAINED BY POLYMERIZING A MASS COMPRISING AN N- PYRIDYL IMIDE OF AN ACID SELECTED FROM THE CLASS CONSISTING OF MALEIC AND CITRACONIC ACIDS AND A POLYMERIZABLE MONOMER HAVING A CH2=C< GROUP. 